Stream Bugs! Gauging Stream Health

OLYMPUS DIGITAL CAMERAAt the end of each summer, staff from the Public Works Department put on their rubber boots and head out to local creeks to collect samples of stream bugs. The scientific term for these creatures is “benthic macroinvertebrates” (benthic = bottom dwelling, macroinvertebrates = large animals without backbones), but that doesn’t exactly roll off the tongue, so we usually just call them “stream bugs.”

These bugs that live on the bottom of streambeds – mayflies, stoneflies, snails and many other invertebrates – are great indicators of a watershed’s health, so we collect bugs annually to see how Kirkland’s watersheds are doing. The bugs are one of the “vital signs” of a healthy ecosystem, as they play a crucial role in the stream nutrient cycle; the absence of certain species in a stream can signal a problem; and bug population fluctuations can indicate a change (good or bad) in a stream.

Once we finish collecting in each stream, the bug samples are shipped off to a lab where they are sorted, analyzed and used to calculate the benthic index of biotic integrity (B-IBI), also called “the bug index.” This index is a synthesis of a lot of information to assess the biological condition, or health, of streams. The bug index is composed of ten “metrics.” The metrics measure different aspects of stream biology, including the diversity of bug species, number of bugs, and presence of bugs that are tolerant and intolerant to pollution, reproductive strategy, feeding ecology, and population structure.

By annually calculating the bug index for Kirkland’s streams, we can see if streams are changing over time. When bug index values are lower than expected, we can investigate what is happening in the watershed that might be degrading stream health.